The present invention relates to an induction heater wherein material is heated by contact with an inductively heated heating element.
GB 2163930 (The Electricity Council) discloses an induction heater having an alternating current carrying conductor extending along an axis. A core means substantially encircles said axis to guide magnetic flux resulting from an alternating current in the conductor. The heating element is an electrically conducting closed loop which encircles the magnetic flux in the core means and so is heated by electrical current induced therein.
Two of the embodiments disclosed in GB 2163930 are shown in FIGS. 1 and 2 of the present specification. In the embodiment of FIG. 1, the conductor 1 forms an axis about which is provided a ferromagnetic core 4. The core 4 is enclosed within a metal skin formed from concentrically aligned inner cylinder 5 and outer cylinder 7 and end plates 6 and 9. In this way, the skin forms a closed electrically conducting loop about the core 4. Alternating currents set up in the conductor 1 by toroidally wound transformer 8 set up an alternating magnetic flux which is guided by the core 4. In turn, the alternating flux in core 4 induces currents to flow around the above mentioned electrically conducting closed loop. Material to be heated is placed within the inner cylinder 5 and is heated by the energy produced in the cylinder by the induced currents. The structure comprising the cylinders 5 and 7 and core 4 can be rotated in the direction of the arrow A. In this way the material to be heated is moved into and out of contact with the cylinder 5 to allow uniform transfer of the heat from the cylinder to the material to be heated.
FIG. 2 shows a continuous flow induction heater. A motor 21 rotates a screw structure 22 in the direction of the arrow A. The screw structure 22 comprises an outer wall 23 which has a spiral slot cut in it to receive screw flight 24. The structure 22 also has an inner wall 25. A toroidal ferromagnetic core 26 is sandwiched between the inner and outer walls 23, 25. An electrically conducting conductor 1, corresponding to that shown in FIG. 1 runs along the axis of the structure 22. As in the embodiment of FIG. 1, a magnetic flux is induced in the core 26 by an alternating current in the conductor 1; this magnetic flux, in turn, induces electrical currents to flow in the walls 23, 25 and the screw flight 24 of the structure 22. The structure 22 is located within a can 28 having an inlet 29 and outlet 30 as shown. Consequently material entering at 29 contacts the structure 22 and is urged towards outlet 30 by the screw flight 24 as the structure 22 is rotated. The material is heated while in contact with the structure 22.